The thesis is devoted to the solution of an actual problem, namely, finding out the mechanisms of luminescence processes in nanocomposite materials with embedded nanoparticles, taking into account the influence of spatial confinement on the luminescence of nanoparticles.
Thermalization length and distribution of electrons by energies are critical for observing of luminescence in nanoparticles. Based on calculations of the YVO4 energy band structure by the method of projection connected waves in parabolic approximation the distribution of electron by kinetic energies after electronic excitations multiplication in YVO4 was received, showing that electrons are mainly localized in the bottom of conduction band. This allows us to neglect the influence of the thermalized electrons leaving nanoparticles on the luminescence of polystyrene matrix.
Mechanisms of scintillation process in polymeric film nanocomposites based on the polystyrene matrix with activators (n-terphenyl and POPOP) and embedded dielectric nanoparticles of fluorides MeF2 (Me = Ba, Ca, Sr), LnF3 (Ln = Ce, Gd, La), phosphates (LaPO4-Pr) and oxides (YVO4: Eu) of different sizes and different weight concentrations. X-ray excited luminescence spectra of polystyrene composites with embedded inorganic nanoparticles contain two bands with maxima at ~350 and ~420 nm, and reveal decay time constant ( ~ 3 ns), which coincide with the parameters of X-ray excited luminescence of polystyrene scintillator exceeding the intensity of luminescence polystyrene emission without nanoparticles more than an order of magnitude.
It has been found out that if the nanoparticle sizes exceed the length of mean free path of electron, then a slow component appears in decay luminescence kinetics of the composite, which corresponds to the decay constant of the material from which nanoparticle is produced, indicating about re-absorption of the intrinsic (BaF2, SrF2) or impurity (LaPO4-Pr) emission by nanoparticles embedded in the polystyrene matrix.
Polystyrene composites with embedded nanoparticles of LaF3, LaF3-Gd, GdF3, which have no intrinsic luminescence, show enhancement of X-ray exited luminescence intensity by ~20 times with the spectral composition of emission and the decay time constants characteristic for luminescence polystyrene. Presence of scintillation response of nanocomposite scintillators with imbedded non-luminescence nanoparticles confirms that the main mechanism of scintillation origin is the excitation of a polystyrene matrix by electrons, which are formed by the mechanism of photoelectric effect in nanoparticles under ionizing radiation influence.
Based on the investigations of luminescence spectral characteristics, its decay kinetics, and the simulation of luminescence processes, the main mechanisms of excitation of polystyrene nanocomposites with imbedded nanoparticles were determined: 1) re-absorption of nanoparticle luminescence by a polystyrene matrix or its activators; 2) resonance mechanism of energy transfer from nanoparticles to polymer matrix; 3) electronic mechanism of excitation due to electron escape from nanoparticle due to the photoelectric effect. The mechanisms 1 and 2 are deter¬minative for large nanoparticles embedded in polystyrene matrix, mechanism 3 for small-size nanoparticles, when the free path length is larger than nanoparticle size.
A number of semiconductor compounds, in particular CsPbX3 perovskites (X = Cl, Br, I), attracting attention of many researchers in view of their possible use as solar cells, LEDs, etc., have some disadvantages connected is with hygroscopicity and/or photoblanching, and, accordingly, need protection from the negative effects of the external environment. This paper presents the results of studies of the conditions for microphase formation in crystalline matrixes on the example of phase formation of K2LaCl5 and LaCl3 in the KCl and NaCl matrixes, respectively, during the growth of crystals with following long-time annealing.
Formation of CsSnBr3 microphase in CsBr-Sn crystals in the process of temperature annealing and in Cs4SnBr6 crystals as a result of the solid state decay on the CsSnBr3 and CsBr phases by the characteristic luminescence parameters and microscopic studies was revealed. CsPbBr3 nanocrystals with a size of ~200 nm, embedded in polymeric granules in the size of ~1 microns have been obtained. Temperature dependences of luminescence intensity of the bound and self-trapped excitons of CsPbBr3 nanocrystals embedded in polymeric granules can be used to determine the temperature of microbiological objects in the temperature range of 77–300 K.
